The overall research objective is to investigate certain genetic aspects of a widespread, complex phenomenon in Drosophila melanogaster known as "hybrid dysgenesis". A number of aberrant traits, including sterility, high rates of mutation and male recombination are frequently induced in hybrids between different incompatible strains due to cytoplasm-chromosome interactions. The genetic mechanisms involved in the determination of the two interacting components will be investigated with respect to one of two identified systems of hybrid dysgnesis, the P-M system. More specifically, the properties of putative transposable elements called P factors, which constitute one component of the system, will be studied together with the corresponding regulatory system. Special emphasis will be placed on studying the frequency of transposition events and the factors responsible for their control. Some implications of this system for population and evolutionary genetics will also be considered. Hypotheses will be tested concerning the mode of evolution of dysgenesis potential and the rapid spread of P factors in natural populations. The methodology employs conventional genetic Drosophila techniques, but informal collaboration with laboratories specializing in molecular genetic techniques is planned. There is considerable potential for the application to human health of basic research on transposable element systems and their regulation, if such systems prove to exist in man. However, the specific nature of such application awaits the results of future research.